Resource competition is a fundamental interaction in biology, occurring when organisms require the same limited resources for survival and reproduction. These resources can include necessities like food, water, light, space, or even mates. The presence of one organism reduces the amount of a shared resource available to others, impacting all involved. This struggle shapes how species interact and influences ecosystem structure and function.
Categorizing Competition
Biologists categorize resource competition by the identity of the competing organisms. Intraspecific competition occurs among individuals of the same species. For example, two oak trees compete for sunlight and soil nutrients, and male deer vie for mates during the rutting season. This type of competition helps regulate population sizes and drives adaptations within a species.
Interspecific competition, in contrast, occurs between individuals of different species. Lions and hyenas, for instance, compete for the same prey on the African savanna. Different plant species in a forest might compete for available light, with taller trees shading out shorter ones. This competition can significantly alter population sizes and influence species distribution within an ecosystem.
Mechanisms of Competition
Resource competition manifests through distinct mechanisms. Exploitative competition, sometimes called scramble competition, involves an indirect interaction where organisms consume resources, making them unavailable for others. For example, algae consume water nutrients, and plants absorb soil nutrients, leaving less for neighboring plants. This form of competition often rewards organisms that claim the resource first or are more efficient at acquiring it.
Interference competition, on the other hand, involves direct interactions where one organism actively prevents another from accessing resources. This can include aggressive behaviors like an animal chasing another from a food source. Certain ant species can plug the entrances of rival colonies to prevent foraging. In plants, interference can occur through allelopathy, where chemicals are released to inhibit the growth of other plants.
Ecological Impacts
The consequences of resource competition extend throughout ecosystems, influencing species interactions, population dynamics, and evolutionary trajectories. The competitive exclusion principle, attributed to G.F. Gause, states that two species cannot indefinitely coexist if they compete for the exact same limited resources. In laboratory experiments, for example, Paramecium aurelia outcompeted Paramecium caudatum with a shared food supply. This principle suggests that one species will eventually outcompete the other if their niches completely overlap.
To avoid such exclusion, species often evolve strategies like resource partitioning, which allows them to coexist by utilizing different aspects of a resource or using it at different times or places. Bird species in a tree, for instance, might feed in different sections or on different types of insects. Lizards in the Caribbean, despite eating similar insect prey, inhabit different microhabitats, such as the forest floor versus tree branches. This division of resources minimizes direct competition and supports biodiversity.
Competition also directly affects population dynamics by limiting growth and influencing population size. As a population grows, resources become scarcer, leading to increased competition that can reduce birth rates and increase mortality. This density-dependent regulation helps control population sizes. Over time, competition drives evolutionary changes, favoring individuals with traits that enhance their competitive ability. This can lead to character displacement, where competing species evolve more divergent traits in areas where they co-occur, such as the varied beak sizes in Galapagos finches that allow them to specialize on different seed types.